The factors that initiate the conversion of a proliferative population of postembryonic skin epithelial cells into a non-proliferative population are being identified. Soluble and insoluble proteins at each stage of the maturation process are being isolated and characterized. Transglutaminase from both a proliferative and a non-proliferative population of skin epithelial cells is being purified, and the role of the transglutaminase in the maturation process of postembryonic skin epithelial cells is being evaluated. The role of the skin endothelial cell in the regulation of skin epithelial cell growth is being studied. BIBLIOGRAPHIC REFERENCES: Karasek, M. A.: "In Vitro Growth and Maturation of Epithelial cells from Post-embryonic Skin". J. Invest. Derm. 65, 60 (1975). Karasek, M. A. and Charlton, M. E.: "Mechanisms of Epidermal Wound Repair". In vitro 10; 338 (1975).